1. Field of the Invention
The present invention relates to a rotor for small motors, which permits electrically satisfactory coupling of the ends of a wound wire with the leg parts of a commutator in an easy operation and a manufacturing method therefor.
2. Description of the Related Art
Connection of each commutator segment and a wound wire end according to the prior art will be described with reference to FIG. 7. FIG. 7 shows a schematic perspective view of the commutator unit of a small motor. In the drawing, reference numeral 11 denotes the shaft of a rotor; 22, a commutator segment; 24, a commutator core; and 26, a commutator leg part. Thus the commutator unit is composed of commutator segments 22 arranged over a resin-made commutator core 24 and commutator leg parts 26, each formed integrally with and at the end of a commutator segment 22 for connecting a wound wire end. FIG. 8 shows a profile of the commutator unit shown in FIG. 7 in a state of being coupled with a wound wire end. The commutator leg part 26, as illustrated, is caused to press down a wound wire end by being bent toward the commutator segment, and is spot-welded.
FIG. 9 shows a varistor alone on its right part and the varistor in a fitted and connected state in the left part. In a small motor having a commutator, when a brush in sliding contact with the commutator passes between commutator segments, an arc is generated, and this arc may jam communication equipment or shorten the useful life of the brush. To solve these problems, fitting a varistor to the rotor of the motor as a spark suppressing element is a known art. An example of such varistor has the shape shown in the right part of FIG. 9. Its overall shape is a doughnut-like disk, and has as many electrodes as the magnetic poles of the rotor, i.e. as many as the commutator segments. Each electrode of this varistor 21 is soldered onto one or another of the commutator leg parts 26. This soldering not only electrically connects the varistor 21 but also is mechanically fixed concentrically with the commutator unit 20.
A wire as a conductor for use in electronic parts, including wound wires for such small motors, usually has an insulating coat, consisting of an insulating material such as urethane, polyester or the like. Whereas the wound wire of a small motor requires electrical and mechanical connection of its ends to each commutator leg part, if a material with a low melting point is used as the insulating coat of the wound wire, the wound wire ends and each commutator leg part have to be arc-coupled to melt and remove the insulating coat by the arc heat, and accordingly electrical connection can be adequately established without needing any special work.
However, where a material of a high melting point is used as the insulating coat of the wound wire, it is difficult to melt by the arc heat, resulting in the problem of impossibility to establish adequate electrical connection. Moreover, toxic gas may be generated by the burning of the insulating coat, necessitating a pollution-preventive measure.
An object of the present invention, therefore, is to solve the problems noted above and make possible adequate electrical connection with commutator leg parts even if a high-melting-point material difficult to be melted by the arc heat is used as the insulating coat of the wound wire.
Another object of the invention is to make it possible to choose the most suitable material for the commutator leg parts to be connected to the insulator-coated wire and thereby to enhance the reliability of connection by virtually limiting the wire material, even though many different kinds of insulator-coated wires are used, to copper alone by stripping the insulating coat.
A rotor for small motors and a manufacturing method therefor according to the invention are such that a plurality of rotor magnetic poles of a salient-pole configuration and a commutator unit are provided on the shaft of the rotor, each of the rotor magnetic poles being composed of a winding around a laminated core and each of both ends of each wound wire being connected to a commutator leg part coupled with a tip of a corresponding commutator segment of the commutator unit. The leading end of a wire to be wound fed from a coil winder is wound around one of commutator leg parts a first prescribed number of turns, then wound around a corresponding salient pole a second prescribed number of turns, thereafter similarly wound successively around other commutator leg parts and other salient poles, and wound around the same commutator leg part around which the leading end of the wire to be wound was first wound; and then the wound wire is cut. Only the portions that will be wound around the commutator leg parts in synchronization with the feed of the wire to be wound from the coil winder are stripped of their insulating coat prior to being wound, and the wound portions of the commutator leg parts are welded.